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venturi burner air intake


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I have a DIY forge and venturi burner. Everything works really well and does what I need it do. However, If I ever turn the forge off and turn it back on before it cools down completely, it performs poorly. A flame comes out of the front of the opening about 6-8 inches, the overall sound has a higher whining sound and the burner pipe begin to heat up and glow red. If I allow the forge to cool down completely, this problem does not occur. From what I've read, this is a poor air intake issue. Also note, the forge is only open on one end. This is primarily due protecting a cinder block wall from the heat ( needs to be close due to space). So, is there a way to allow more air to be pulled in so the restart mixture of air:fuel is as clean as an cold start? Also, I don't mind opening the rear of the forge if this will help the air flow, but what is recommended to protect the wall from direct heat? Thanks!

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Can you post a picture or two of your current setup? It'll help others here see exactly what you're seeing.

If the air intake(s) are sucking in hot air, you're probably combusting the gas further up the pipe than ideal, which is why you're getting the results you're getting. That's of course if your burners are coming in through the top. A side burner wouldn't suck in as much hot air, as heat rises.

But since I'm new to the game I can only speculate. 

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A whistling/chirping sound and a hot mixing tube are classic signs of the flame burning inside the burner tube rather than at the end of it.  There are a number of reasons this can happen, but with the information you gave I'm guessing your burner is top mounted and pointing down rather than tangentially.  Once you shut the burner off the heat inside the forge starts to go back up through your burner tube (chimney effect).   Now if you restart your burner, the end of the mixing tube closest to the forge chamber becomes hot enough for ignition to take place there instead of at the end of the burner.  Once you let everything cool down to ambient temperature then the mixing tube is below the ignition temperature for your fuel/air mix and it once again burns at the end as it should.

There may be some ways to keep this from happening depending on your burner design.   If you can snap some pics of the burner and post them it will help.  Try to get at least one of the flame in the forge shortly after starting up, one while experiencing the problem, and one of the air intake area.

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